This study aimed to characterize the developmental trajectories of different cognitive component processes underlying planning decisions. Participants (ages 8-25 years) completed a planning task called Four-in-a-row. We used computational modeling to distinguish between three cognitive component processes of planning: planning depth, heuristic quality, and attentional oversights, each of which three contributed to better playing strength, but differed in their developmental trajectories. Specifically, from early to mid-adolescence, heuristic quality rapidly improved and contributed to better playing strength. From mid to late-adolescence, planning depth increased and supported better playing strength. Fewer attentional oversights were associated with better playing strength and this relation did not show age differences. Together, these results reveal sequential development of the cognitive component processes underlying planning, with early refinement of heuristic strategies, and gradual increases into young adulthood in the number of considered future actions, states, and outcomes. These findings provide a more complete account of the development of planning and its component processes.